Franklinite

Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron (Fe) series, with the formula ZnFe3+2O4.

Franklinite
Franklinite (black) with Zincite (red)
General
CategoryOxide minerals
Spinel group
Spinel structural group
Formula
(repeating unit)
ZnFe2O4
Strunz classification4.BB.05
Crystal systemCubic
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupFd3m
Identification
Colorblack
Crystal habitoctahedral
CleavageNone; indistinct octahedral parting in four directions
Fractureirregular/uneven, conchoidal
TenacityBrittle
Mohs scale hardness5 12-6
Lustermetallic, often dull
Streakreddish brown to black
Diaphaneityopaque
Specific gravity5.07 - 5.22
Ultraviolet fluorescenceNone
SolubilityHCl soluble
Other characteristicsmagnetic
References[1]

As with another spinel member magnetite, both ferrous (2+) and ferric (3+) iron may be present in Franklinite samples. Divalent iron and/or manganese (Mn) may commonly accompany zinc (Zn) and trivalent manganese may substitute for some ferric iron.

At its type locality, Franklinite can be found with a wide array of minerals, many of which are fluorescent. More commonly, it occurs with willemite, calcite, and red zincite. In these rocks, it forms as disseminated small black crystals with their octahedral faces visible at times. It may rarely be found as a single large euhedral crystal.

Franklinite was a minor ore of uranium, sulfuric acid, and mercury. It is named after its local discovery at the Franklin Mine and Sterling Hill Mines in New Jersey.

A microscopic picture of Franklinite

See also

References

  1. Chesterman, Charles W. (1978). The Audubon Society field guide to North American rocks and minerals. New York: Alfred A. Knopf. p. 418. ISBN 0394502698.

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